1. Field of the Invention
This invention relates generally to a method of manufacturing wellbore tools and specifically to liner hangers which are used in subterranean wellbores to couple portions of a casing string together.
2. Description of the Prior Art
In the oil and gas industry, a variety of wellbore tools are used which are run into wellbores for temporary or permanent placement in a desired location relative to selected geologic formations, other wellbore tools, or nested wellbore tubulars. The conveyance mechanisms available to run such wellbore tools into wellbores include wirelines, coiled tubing strings, and tubular workstrings. The severe space limitations within wellbores, and wellbore tubular strings such as wellbore casing strings and wellbore production tubing, frequently require that the components of the wellbore tool be carried on the interior or exterior cylindrical surface of a wellbore tubular member. When tubular workstrings are used as a conveyance mechanism, wellbore tools usually include a tubular body which is threaded at its uppermost and lowermost ends for connection in a workstring at a desired location. The components of the wellbore tool are most frequently carried about the cylindrical exterior surface of the tubular body, and are sized to maintain the wellbore tool out of physical contact with wellbore surfaces and nested wellbore tubular strings during a running mode of operation. Wellbore tools such as bridge plugs, packets, and liner hangers are located at a desired position with the wellbore, and then urged from a radially-reduced running condition to a radially-expanded gripping or sealing condition.
To enhance safety and maximize wellbore tool life, it is frequently required that portions of the wellbore tool be secured to the tubular body as permanently as possible. This is especially true for load bearing tools, such as some packers, and all liner hangers. In the case of liner hangers, large axial loads are transferred from the tubular body to a gripping assembly which is carried circumferentially about the exterior surface of the tubular body, and which includes cone rings and gripping slips. The axial load is transferred from the tubular body, through the gripping assembly, to a nested wellbore tubular.
To enhance safety and ensure wellbore tool integrity and longevity, two general manufacturing options exist: forming all, or portions, of the wellbore tool directly into the tubular body by machining; or welding all, or portions, of the wellbore tool to the exterior or interior surface of the tubular body. Machining requires the use of expensive and complex metal working equipment, thus restricting manufacturing and assembly operations to dedicated manufacturing sites with access to a work force which includes highly skilled machinists. Machining also adds considerably to the expense of manufacturing operations. The use of welding to secure selected wellbore tool components to the exterior or interior surfaces of a tubular body has similar disadvantages. Manufacturing and assembly operations are generally restricted to selected manufacturing facilities which have access to highly skilled welders. Welding components to a tubular body can weaken the structural strength of the tubular body, and jeopardize the performance and longevity of a wellbore tool. Therefore, welding operations ordinarily require careful inspection to ensure that the tool contains no defective welds.
In the oil and gas industry, manufacturing operations are highly centralized, with several cities and locations being the source of a large number of wellbore tools used all around the globe at remote locations. Typically, wellbore tools are manufactured entirely at one location, and are shipped in final and completed form to a well site for immediate use. It is not uncommon for wellbore tools to be ordered for immediate delivery and use; therefore, manufacturers are, as a practical matter, required to have inventory of assembled tools on hand for immediate shipment to remote locations. Of course, having valuable corporate capital tied up in manufactured and assembled equipment runs contrary to the principles of just-in-time manufacturing which dictate that only minimal amounts of corporate capital be tied up in inventory.
The fact that many wellbore tools are manufactured entirely at a selected small number of locations, and shipped to remote locations around the globe, means that, for many wellbore tools, shipping expenses comprise a considerable portion of the total cost to the end user. Therefore, decentralized manufacturing and assembly would probably result in both lower prices for end users, and lower costs for manufacturers, but would require that complicated machining and welding operations be performed at a great number of locations around the globe. For the reasons set forth above, decentralized machining or welding operations are impractical, since they require capital-intensive equipment and highly skilled workers.